Thirty-two subjects with unilateral cerebral tumors were assessed for the use of hypotheses and cognitive strategies during a visual discrimination task. Subjects with frontal lobe lesions attained fewer concepts and used fewer appropriate hypotheses than subjects with tumors confined to the posterior hemisphere, although there was no difference in total hypotheses used. Lose-stay errors were committed with greater frequency among patients with frontal lobe lesions, although not all subjects with frontal lobe tumors exhibited this error tendency. The results of hypothesis sampling and a second visual discrimination transfer task suggested that the frontal lobe deficit was related to difficulty in attending to multiple cues and in monitoring feedback to segregate relevant from irrelevant sources of information. © 1983.